1. Field of the Invention
The present invention relates to a clamp for suspending a cable and a method for attaching the clamp to a cable. More particularly, it related to a hinged bushing suspension clamp for suspended a cable and a method for attaching the hinged clamp to a suspended cable.
2. Description of the Related Art
Power cables are frequently suspended aerially from poles or other support structures. An aerial arrangement of such cables has the advantages of relatively simple and flexible installation having a limited ground footprint, and permits space substantially below the cables to be used for other purposes. An aerial arrangement also separates the cables from contact with people or roaming ground animals. Spatial separation is particularly important for high tension electrical power transmission cables for safety reasons. Separation of any cable helps protect the cable from damage caused either inadvertently or through malicious vandalism.
Although aerial cables are relatively safe from ground-based sources of damage, they are subject to environmental wear and damage, principally due to winds. Well known in the art are problems caused by aeolian vibration which is a high frequency, low amplitude vibration caused by laminar winds passing across the line, as well as galloping which is a low frequency, high amplitude wind-induced cable motion. Aeolian vibration, galloping, and other wind action can produce cable damage especially at the suspension points where cable clamps and other supporting devices mechanically stress the cable. Cable damage in the form of abrasion, wear, and fatigue can occur especially at the clamping points. The fatigue of the conductor at the clamping point is directly related to the amount of bending at this location. The amount of bending a conductor can endure without failure is known as its “Maximum Safe Bending Amplitude.” This value is normally given in “mils” and varies by the amount of tension in the transmission line.
One prior art cable clamp found in U.S. Pat. No. 6,595,472. That cable clamp is opened and hinges by means of two bolts at the bottom of the clamp. The conductor is installed down between the “mounting ears” and sits into a metal groove with bushings at its exit. Three bolts are then tightened around the conductor. However, if the three bolts are not tightened in a method to keep the clamps halves parallel, the ears will end up with an angle between. This will not allow the attachment pin to install through the holes in both ears. Also, a tightening sequence must be followed between the upper bolt and lower bolts to ensure even load on the conductor. While this prior art clamp is difficult to install on un-energized transmission lines, it is even more difficult to install on energized transmission lines because “hot-line” tools must be used.
Another disadvantage of this design is that if installer does not sequentially torque the bolts to an equal amount, a bending moment occurs on the bolt/bolts with less torque. If the two bottom bolts are torque excessively, this makes the top (single) bolts experience a bending moment making it difficult to turn and tighten. This hinge design involves repeated tightening of bolts, in small torque increments, until desired installation torque is achieved.